The research looked at roughly 15,000 births that took place in Sweden between 1992 & 2009, including about 2,500 women who had had weight loss surgery. On average, the women delivered about five years after the surgery.

After controlling for age, smoking and other factors that could influence pregnancy complications, the researchers found that 10 percent of children born to women who had undergone bariatric surgery were delivered prematurely, compared with 6 percent in the other group.

One interesting note, mothers who had had weight loss surgery did have one advantage: they were less likely to deliver excessively large babies. The researchers noted that excessive fetal growth is strongly linked to obesity and often driven by high blood sugar levels and insulin resistance, both of which are improved by weight loss surgery.